1. Field
Exemplary embodiments of the present invention relate to semiconductor design technology, and more particularly, to a cell array, a memory, and a memory system including the same, which is capable of counting and storing the number of activation times that each word line is repeatedly activated, and detecting whether the number of times for a specific word line is equal to or greater than the number of reference times.
2. Description of the Related Art
As an increase in the degree of integration of a memory, intervals among word lines included in the memory, such as DRAM, are reduced. As the intervals among the word lines are reduced, a coupling effect between adjacent word lines is increased.
Meanwhile, whenever data is input/output to or from a memory cell, a selected word line is toggled between an activated state and a deactivated state. As described above, as the coupling effect between adjacent word lines is increased, data of a memory cell connected to word lines adjacent to the excessive activated word line may be degraded. Such a phenomenon is called word line disturbance or word line hammer. Due to the word line disturbance, before a memory cell is refreshed, data of the memory cell may be damaged.
FIG. 1 is a diagram illustrating a part of a cell array in DRAM for explaining the word line disturbance.
In FIG. 1, ‘WLL’ corresponds to a word line excessive activated, and ‘WLL−1’ and ‘WLL+1’ correspond to word lines adjacent to the ‘WLL’, that is, word lines ‘WLL−1’ and ‘WLL+1’ are disposed adjacent to the excessive activated word line ‘WLL’. Furthermore, ‘CL’ indicates a memory cell connected to the ‘WLL’, ‘CL−1’ indicates a memory cell connected to the ‘WLL−1’, and ‘CL+1’ indicates a memory cell connected to the ‘WLL+1’. The memory cells include cell transistors TL, TL−1, and TL+1 and cell capacitors CAPL, CAPL−1, and CAPL+1, respectively.
When the word line ‘WLL’ is activated or deactivated, voltages of the word lines ‘WLL−1’ and the ‘WLL+1’ are increased or decreased due to a coupling phenomenon among the word lines ‘WLL’ and ‘WLL−1’ and among the word lines ‘WLL’ and ‘WLL+1’. Accordingly, the amount of charges charged in the cell capacitors CAPL−1 and CAPL+1 is affected, so that data of the memory cells CL−1 and CL+1 is degraded.
Furthermore, electromagnetic waves, which are generated when the word line is toggled between the activated state and the deactivated state, allow electrons to be introduced into cell capacitors of the memory cells connected to adjacent word lines or to be discharged from the cell capacitor, so that data may be damaged.
To substantially prevent degradation of data due to the word line disturbance, it may be necessary to provide a scheme for detecting the excessive activated word lines, and thus a method for counting the number of activations for each word line may be desirable.